Concatenated SMS extended symbols at segments border - what is correct split method?

Question

For concatenated SMS messages (in GSM encoding), if extended table symbol (one of these: }{[]|~^\€) is placed at the end of segment, what is correct way to split such message:

1. Leave first byte of symbol (0b) at the end of segment and put second byte to the beginning of next one, and so fill all available bytes of UD (which seems logically correct)

OR

2. Move whole symbol bytes to the next segment and leave unused byte at the end?

I didn't found any clarification neither in SMPP 3.4 specs or implementation guide nor in GSM 03.38 specs, so assume that method selection is up to content provider or sending software.

Empirical

please have a look at my answer and provide me with some feedback so that we could close this issue for you and for anyone who might come across this in future – Vladimar

Answer 1

When you are using a 7-bit encoding, split when you reach 153 characters (whether that is in-between the 1B and the next character or not).

Zettazeugma

Answer 2

I can't think of any reason to prefer option 2 (leave unused byte at the end).

The message should not be rendered unless it's completely received by the subscriber's device. Furthermore, nothing is even represented by 1B septet in GSM7, so even if a device tried to render something unexpected it would fail.

Vladimar